This invention relates to ion vapour deposition (herein IVD) and relates to a method of and apparatus for applying coatings by IVD.
The invention has particular reference to the application of coatings to optical lenses of the type used in spectacle frames, and which mainly will be corrective lenses, but could be plain lenses, but in fact the invention it is believed will have a much wider application, at least in specific aspects thereof, such that the invention can be applied to the application of coatings to other articles.
The lenses to which the invention applies may be of glass or plastics material.
As the main application as will be understood relates to the application of IVD coatings to spectacle lenses, reference will be made hereinafter exclusively or mainly to such a product and the coating thereof.
The IVD process comprises the placement of an article to be coated in a chamber in which is provided a target of the coating material. Negative electric bias is applied to the target, and the chamber is filled with an inert gas, such as argon. Ionisation of the gas takes place, and the gas positive ions bombard the target by virtue of being attracted thereto due Ira the negative electric bias on the target. Sputtering of the target takes place which is a phenomenon resulting in the release of particles of the target material into the chamber atmosphere. These particles then deposit on the surface of the article to be coated and may be induced to deposit on the article by virtue of an electric bias on the article or in the region of the chamber surrounding the article, and so a coating is built up.
IVD processes are of course well established for many products, and are typically used for metallic products which require to be coated to a high degree of accuracy, and where the articles have to be used in controlled environments or in situations where the performance of the articles is critical. For example IVD coated articles such as screws, nuts and bolts may be used in the aircraft industry, in military applications, or in space vehicle applications. The prior devices use a target with one material attached to it. Therefore only one single material can be sputtered from the target.
The use of IVD for the coating of spectacle lenses is also known. Coatings on spectacle lenses perform several functions. Firstly, a reflection control coating serves to allow as much light of wavelength in the visible range through the lens into the eye as possible, whilst reflecting as much light which is in the harmful wavelength region, such as UV light, from the eye as possible. Other IVD coatings serve to provide a hard protective surface to protect the lenses from scratching and the like.
Generally speaking, the equipment which is used for IVD coating of lenses is large and is expensive, and requires considerable investment in the part of a processor, and in commercial terms when a person orders a pair of spectacles from an optician, he submits the prescription to a lens manufacturer, but the lens manufacturer in turn will pass on the lenses to the IVD coating processor who will coat the lenses as required. Coating in the conventional machine can take as much as one hour.